Thyroxine and negative feedbackSpec 7.3
In short
Thyroxine is a hormone made by the thyroid gland that controls metabolic rate, the rate of the chemical reactions in the body. Its level is kept steady by negative feedback. A low level stimulates the hypothalamus to produce TRH, which makes the pituitary gland release TSH, and TSH makes the thyroid produce thyroxine. A normal level inhibits TRH and TSH.
Thyroxine is made by the thyroid gland. It controls metabolic rate, which is the rate of the chemical reactions in the body. Its level is kept steady by negative feedback.
- Negative feedback
- A change in a level causes a response that reverses the change and brings the level back to normal.
- A low level of thyroxine stimulates the hypothalamus to produce TRH.
- TRH causes the pituitary gland to release TSH.
- TSH acts on the thyroid gland to produce thyroxine.
- The thyroxine level rises back to normal.
- When the thyroxine level is normal, thyroxine inhibits the release of TRH and the production of TSH. This stops the level rising too far.
TRH is made in the hypothalamus and TSH is released from the pituitary gland. Mixing up the two organs loses marks.
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How are hormones transported from endocrine glands to target organs?
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In the blood (plasma).
Which gland produces insulin?
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The pancreas.
Name the four effects of adrenalin. (Higher)
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Increased heart rate, increased blood pressure, increased blood flow to the muscles, and raised blood sugar level.
Which hormone does the pituitary release to make the thyroid produce thyroxine? (Higher)
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TSH.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026